Historically, investigations of "reduced" visual systems have made valuable contributions to our knowledge of normal vision; for example, studies of color vision anomalies were important in the development of the trichromatic basis of normal color vision. Analogously, our understanding of binocular vision processes should benefit from investigations of subjects with reduced stereopsis. The present application, therefore, proposes investigations of positional disparity processing in monkeys with stereo-deficiencies which occur as a consequence of abnormal binocular visual experience, during early life. Three experimental rearing procedures will be used, each of which causes anomalies of binocular vision without significant secondary anomalies (strabismus or amblyopia). (1) Short-term bilateral form deprivation, to uniformly prevent adequate stimulation of all disparity processing systems. (2) Short-term optical dissociation of binocular vision, which presumably alters binocular vision through suppression mechanisms. (3) Long-term unilateral, alternating, defocus to selectively degrade binocular positional disparities, without permanent alterations of monocular spatial vision. The assessment of the vision of the control and experimental monkeys will involve a series of psychophysical measurements of basic functions of monocular (spatial contrast sensitivity and the accuracy and precision of fixation) and binocular vision (interocular alignment, fusional vergence ranges, binocular summation for spatial gratings, local steropsis with narrow-band, spatially filtered stimuli, and global stereopsis with dynamic random-dot stereograms). Correlations of the results of the various functional measures should significantly increase our knowledge of normal binocular vision, with respect to the nature of the interactions between disparity vergence and stereopsis, the independence of crossed and uncrossed disparity mechanisms, the functional differentiation between fine and coarse stereopsis, and the dependence of global stereopsis on normal local stereopsis mechanisms. In addition, the results of these studies should provide new insights into the dysfunctions of binocular vision associated with strabismus and amblyopia in children.